Wireless communication apparatus

ABSTRACT

The wireless communication apparatus includes transmitter modules and receiver modules for carrying out transmission/reception via a plurality of antenna beams formed by an adaptive array antenna between stations. The apparatus is provided with an end time detecting section and a maximum reception end time is detected by detecting section based on reception signals on the receiver modules. A reception end signal is generated from a notifying section, when current time counted by a counter is reached to the maximum reception end time. The transmission enabling section causes the transmitter modules to transmit data in response to the reception end signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of priorityunder 35 USC §120 from U.S. Ser. No. 10/156,111, filed May 29, 2002 nowU.S. Pat. No. 7,158,501 and is based upon and claims the benefit ofpriority under 35 USC §119 from the Japanese Patent Applications No.2001-160928, filed May 29, 2001, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication station and,more particularly, to an access point which communicates with wirelesscommunication stations via a plurality of channels.

2. Description of the Related Art

There is known a wireless LAN system making communication between anaccess point (AP) and a plurality of wireless communication stations(STAs). As this wireless LAN system, there is provided a wireless LANsystem (ISO/IEC 8802-11:1999(E) ANSI/IEEE std 802.11, 1999 edition)under the IEEE802.11 standard that defines a CSMA (Carrier SenseMultiple Access). In this wireless LAN system, in general, prior totransmitting a packet to a wireless station, which is so called a targetstation to which the packet is to be transmitted, an access point sensesa carrier for transmitting the packet. However, where a reception statein which a packet including channel reservation information is receivedfrom another station is established, packet transmission to the targetstation is suspended. Where the transmission is suspended, the accesspoint starts transmission of a packet for specifying an address for thetarget station after ending of the packet reception state for theanother station and elapse of a random transmission waiting periodcomputed at a control section of the access point. In this way,processing in which the transmission to the station is suspended, therandom transmission waiting period is elapsed, and the packet istransmitted is referred to as back-off processing.

The target station transmits an acknowledge response (ACK) packet to theaccess point after a predetermined period if data on the received packethas been normal. At the access point, when the ACK packet from thetarget station cannot be received after the elapse of the predeterminedperiod, the control section executes back-off processing, and a packetis transmitted again.

On the other hand, a Space Division Multiple Access (SDMA) method isknown as one of the multiplexing schemes in a wireless communicationsystem. In the SDMA method, a plurality of antenna beams for spatiallydecreasing mutual interference are generated from an adaptive arrayantenna provided at the access point. Therefore, the SDMA method canimprove its communication quality and can achieve simultaneouscommunication between the access point and a plurality of stations. TheSDMA method is applied to a wireless LAN system of the CSMA method,whereby it is expected that an advantage of the SDMA method can beprovided.

However, if the SDMA method is simply applied to the wireless LAN systemof the CSMA method, the following problem occurs.

In the SDMA method, at the access point, there is provided transmitterand receiver modules corresponding to a plurality of antenna beamsformed by an adaptive array antenna. Further, individual controlsections control the transmitter and receiver modules, respectively. Inan ideal communication system provided with the adaptive array antenna,each of the antenna beams can be used for receiving only one signal fromthe target station without being affected from another stations. Thus,if the CSMA is executed for each antenna beam by these individualcontrol sections, back-off processing is executed for each antenna beam.As a result, there can occur a case in which, at the access point, bothof transmission to one station and reception from another station takesplace at the same time. That is, even if the access point attempts toreceive a packet from one station (TE1), when transmission to anotherstation (TE2, TE3) takes place at the same time as the reception, suchtransmission may act as an interference and affect on the reception fromthe station TE1, thus disabling reception.

Where the access point transmits packets to the plurality of stations(TE1, TE2, TE3), no reception state occurs at the access point. Thus, acollision between transmission and reception can be basically prevented.However, when one side of packet to be transmitted to one station TE1 issmaller than that of packet to be transmitted to another station TE2,TE3, even if the access point is placed in a transmitting state fortransmitting the packets to the stations TE2, TE3, respectively, thestation TE1 generally terminates packet reception. Therefore, thisstation TE1 transmits an ACK packet to the access point. As a result,even if the access point could receive the ACK packet from the stationTE1, the access point may not actually receive the ACK packet from thestation TE1 due to an interference caused by the packet transmissionfrom the access point to the stations TE2, TE3. This ACK packet has aneffect on transmission to the station TE2, TE3, and the station TE2, TE3cannot receive a packet from the access point.

Further, at the access point, where an ACK packet is not received fromone of a plurality of stations TE1, TE2 and TE3, for example, onestation TE2, there is a problem that back-off processing is executed atthe access point for transmission and reception between the access pointand the station TE2, and a timing of transmitting a packet to each ofthe stations TE1, TE2 and TE3 during this processing and subsequent isshifted.

The similar problem will occur in the CSMA/CA (Carrier Sense MultipleAccess with Collision Avoidance) method in which communication isautonomously controlled by using a protocol as well as a case of simplyapplying the SDMA (Space Division Multiple Access) method to thewireless LAN system of the CSMA (Carrier Sense Multiple Access) method.That is, in the wireless access point in which the CSMA/CA method hasbeen employed, where a channel to be used has been an adjacent channelor the same channel, there is a problem that signals of the respectivechannels interfere with each other, and a data transmission erroroccurs.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wirelesscommunication station capable of properly carrying outtransmission/reception between the wireless communication station andanother wireless communication station.

According to an aspect of the present invention, there is provided awireless communication apparatus for receiving first and secondreception signals from another wireless communication stations andtransmitting first transmission signal to another wireless communicationstation, comprising:

a receiving section including first and second receiver modulesconfigured to sense first and second reception signals to be set in areception mode, and receive the first and second reception signals fromthe another wireless communication stations in a reception mode;

a responding section configured to respond to an end timing of receivingthe first and second reception signals in the receiving section togenerate a reception end signal;

a transmission section including first transmitter modules configured totransmit the first transmission signal in a transmission mode andinhibit the transmission of the first transmission signal in thereception mode, the transmission section being kept in a waiting statein the transmission mode to wait the occurrence of the firsttransmission signal; and

an enabling section configured to enable the transmission section totransmit the first transmission data signal, the enabling sectioncausing the transmission section to switch into the transmission modefrom the reception mode in response to the reception end signal and tokeep the transmission section in the waiting state, the transmission offirst transmission signal being started in the waiting state.

According to an another aspect of the present invention, there isprovided a wireless communication apparatus for executing collisionaccess control in accordance with Carrier Sense Multiple AccessCollision Avoidance protocol, to transmit and receive data packets usingfirst and second radio channels between the wireless communicationapparatus and the first and second station units, the wirelesscommunication apparatus comprising:

a first wireless communication module section configured to transmit andreceive the data packet in the first radio channel in first transmissionand reception modes, respectively;

a second communication wireless module section configured to transmitand receive the data packet in the second radio channel in the secondtransmission and reception modes, respectively; and

a control section configured to control the second wirelesscommunication module to prevent the second wireless communication modulefrom transmitting the data packet in response to a detection of thefirst reception mode while the first wireless module is receiving a datapacket in the first reception mode.

According to a still another aspect of the present invention, there isprovided a wireless communication apparatus for executing collisionaccess control in accordance with Carrier Sense Multiple AccessCollision Avoidance protocol, to transmit and receive data packets usingfirst and second radio channels between the wireless communicationapparatus and the first and second station units, the wirelesscommunication apparatus comprising:

a first wireless communication module section configured to transmit andreceive the data packet in the first radio channel in first transmissionand reception modes, respectively;

a second communication wireless module section configured to transmitand receive the data packet in the second radio channel in the secondtransmission and reception modes, respectively; and

a control section configured to control the second wirelesscommunication module to transmit a dummy packet and prevent the secondwireless communication module from receiving the data packet in responseto a detection of the first transmission mode while the first wirelessmodule is transmitting a data packet in the first transmission mode.

According to a still another aspect of the present invention, there isprovided a wireless communication apparatus for executing collisionaccess control in accordance with Carrier Sense Multiple AccessCollision Avoidance protocol, to transmit and receive data packets usingfirst and second radio channels between the wireless communicationapparatus and the first and second station units, the wirelesscommunication apparatus comprising:

a first wireless communication module section configured to transmit andreceive the data packet in the first radio channel in first transmissionand reception modes, respectively;

a second communication wireless module section configured to transmitand receive the data packet in the second radio channel in the secondtransmission and reception modes, respectively; and

a control section configured to control the first and second wirelesscommunication modules to sense the first and second radio channels andset the first and second wireless communication modules in a synchronousmode in which the data packets start to be transmitted from the firstand second wireless communication modules at a same time.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram schematically showing a wireless LAN systemaccording to a first embodiment of the present invention;

FIG. 2 is a block diagram schematically showing an access point shown inFIG. 1;

FIG. 3 shows a flow chart illustrating an operation of receiving andtransmitting procedure in the access point shown in FIG. 1;

FIG. 4 is a block diagram schematically showing an adaptive arrayantenna shown in FIG. 1;

FIG. 5 is a block diagram schematically showing details of a maximumreception end time detecting section shown in FIG. 2;

FIG. 6 and FIG. 7 are schematic views each showing a structure of a datapacket to be transferred between an access point and a wireless stationshown in FIG. 1;

FIG. 8 is a block diagram schematically showing details of atransmission enabling section shown in FIG. 2;

FIG. 9 is a block diagram schematically showing a more detailedexemplary circuit of a maximum reception end time detecting sectionshown in FIG. 2;

FIG. 10 is a timing chart illustrating an operation of the maximumreception end time detecting section shown in FIG. 8;

FIG. 11 is a block diagram schematically showing an access pointaccording to another embodiment of the present invention;

FIG. 12 is a block diagram schematically showing an access point and awireless communication station in a wireless LAN system according toanother embodiment of the present invention;

FIG. 13 is a schematic view showing a structure of a control packet tobe transferred between the wireless communication station and the accesspoint in the wireless LAN system shown in FIG. 12;

FIG. 14 is a schematic view showing operation of receiving andtransmitting procedures in wireless LAN system shown in FIG. 12;

FIG. 15A is a block diagram showing disposition of an access point and astation according to another embodiment of the present invention;

FIG. 15B is a view showing a pattern of antenna beams formed in adirection of each station by the access point at a down-link in thesystem shown in FIG. 15A;

FIG. 16A to 16C are time charts illustrating an operation in the systemshown in FIG. 15A;

FIG. 17 is a schematic view showing operation of receiving andtransmitting procedures in the system shown in FIG. 15;

FIG. 18 is a flow chart showing operation of receiving and transmittingprocedures in wireless LAN system shown in FIG. 12;

FIG. 19 is a block diagram showing a circuit configuration of a stationaccording to another embodiment of the present invention;

FIG. 20 is a view showing an entire configuration of a wirelesscommunication system according to a still another embodiment of thepresent invention;

FIG. 21 is a block diagram showing a circuit configuration of a wirelessaccess point shown in FIG. 21;

FIG. 22 is a schematic view showing operation of receiving andtransmitting procedures in the wireless module shown in FIG. 21;

FIG. 23 is a schematic view showing another operation of receiving andtransmitting procedures in the wireless module shown in FIG. 21;

FIG. 24 is a schematic view showing still another operation of receivingand transmitting procedures in the wireless module shown in FIG. 21;

FIG. 25 is a schematic view showing yet another operation of receivingand transmitting procedures in the wireless module shown in FIG. 21;

FIG. 26 is a block diagram showing a modified circuit configuration of awireless access point shown in FIG. 21;

FIG. 27 is a block diagram showing another is a block diagram showing acircuit configuration of a wireless access point shown in FIG. 21;

FIG. 28 is a block diagram showing a circuit configuration of a wirelesscommunication system according to yet another embodiment of theinvention; and

FIG. 29 is a block diagram showing a circuit configuration of a wirelesscommunication system according to yet further embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 1 shows a wireless LAN system in which a space divisionmultiplexing access (SDMA) method is applied as a wireless communicationsystem according to a first embodiment of the present invention. Thiswireless LAN system is constructed in conformance with the IEEE802.11standard (including IEEE802.11a, IEEE802.11b). An access point 1 isinstalled in its specific fixed location, and is connected to a backbonenetwork 5. The access point 1 comprises an adaptive array antenna 2. Theadaptive array antenna 2 generates a plurality of radio waves 3-1 to 3-3(hereinafter, referred to as antenna beams) with their comparativelynarrow directivities to a plurality of stations 4-1 to 4-3.

By means of such antenna beams 3-1 to 3-3, the access point 1 cancommunicate with the plurality of stations 4-1 and 4-3 via thesubstantially same channel or adjacent channel while reducinginterference between stations. That is, communication is executedbetween the access point 1 and the stations 4-1 to 4-3 each inaccordance with the space division multiplexing access (SMDA) method.

In the above-described wireless LAN system, a description is given withrespect to an example in which the access point 1 generates threeantenna beams 3-1 to 3-3, thereby communicating with the three stations4-1 to 4-3 at the same time. However, in the wireless communicationsystem according to the embodiment of the present invention, the numberof antenna beams and the number of stations carrying out simultaneouscommunication may be arbitrarily two or more. In addition, the stations4-1 to 4-3 are generally installed in their fixed locations, but may beincorporated in a mobile unit.

Now, with reference to FIG. 2, a description will be given with respectto the access point 1 shown in FIG. 1 of a wireless LAN system to whichthe space division multiplexing access (SDMA) method according to theembodiment of the present invention has been applied.

As shown in FIG. 2, the access point 1 comprises the adaptive arrayantenna 2 that forms the antenna beams 3-1 to 3-3 oriented to thestations 4-1 to 4-3 to communicate with the station 4-1 to 4-3. Thisadaptive array antenna 2 is connected to receiver modules 11-1 to 11-3.Therefore, reception signals carried by the antenna beams 3-1 to 3-3oriented to these stations 4-1 to 4-3 are received at the receivermodules 11-1 to 11-3. At the receiver modules 11-1 to 11-3, receptionsignals are processed, and reception signals RS1 to RS3 are generated.Processing of this reception signal includes modulation and demodulationof the reception signal.

At the access point 1, transmitter modules 12-1 to 12-3 are connected tothe adaptive antenna 2. At the transmitter modules 12-1 to 12-3,transmission signal s TS1 to TS3 to be transmitted to the stations 4-1to 4-3 respectively are generated, and these transmission signal s TS1to TS3 are supplied to the adaptive antenna 2. The transmission signal sTS1 to TS3 are transmitted to the wireless stations 4-1 to 4-3 by theantenna beams 3-1 to 3-3 formed by the adaptive array antenna 2.

The access point 1 comprises a reception end detecting section 18 and atransmission enabling section 19. In the reception mode for permittingthe receiver modules 11-1 to 11-3 to receive a reception signal from thewireless stations 4-1 to 4-3, the reception end detecting section 18detects a final transfer time in a reception signal in the receivermodules 11-1 to 11-3, thereby generating a reception end signal. Thetransmission enabling section 19 supplies a transmission enable signalto the transmitter modules 12-1 to 12-3 in response to the reception endsignal. That is, the access point 1 is switched from the reception modein response to the transmission mode to the transmission enable signal.The transmission enabling section 19 maintains the transmitter modules12-1 to 12-3 in a transmission disable state in the reception mode, andthe receiver modules 11-1 to 11-3 in a receiving disable state in thetransmission mode. The transmission enabling section 19 switches thetransmitter modules 12-1 to 12-3 from the transmission disable state tothe transmission enable state in response to the transmission enablesignal. In this way, in the transmission enable state, i.e., in thetransmission mode, back-off processing is started in response to thetransmission enable signal, thereby entering a transmission waitingstate in which transmission is waited, and a transmission signal istransferred to each of the wireless stations 4-1 to 4-3. As describedlater, it is preferable that a data packet included in the transmissionsignal have the same packet length so that transmissions from the accesspoint 1 to each of the wireless stations 4-1 to 4-3 terminate at thesame time, and ACK signals are also transferred to the receiver modules11-1 to 11-3 from the wireless stations 4-1 to 4-3 at the same time.

There will be described an example of operation procedures in the accesspoint 1 shown in FIG. 2 with reference to FIG. 3. In the operationprocedures shown in FIG. 3, the data packets each having a same packetsize are transferred between the access point 1 and the wirelessstations 4-1 to 4-3.

In the access point 1, the transmitter module 12-1 is supplied withtransmission data from a transmission data supply section 10 and thetransmission data is transmitted from the transmitter module 12-1 to thewireless station 4-1 in the transmission mode. The access point 1 isswitched from the transmission mode to the reception mode, when thetransmission of the transmission data from the access point 1 to thestation 4-1 is ended, as shown in step S10 of FIG. 3. Thus, the receivermodule 11-1 is prepared to receive ACK signal from the station 4-1, asshown in step S11. In this reception mode, the transmitter modules 12-1to 12-3 are maintained in the transmission disable state. Thetransmission data is supplied to the transmitter 12-2 and 12-3 so thatthe transmission of the transmission data is prepared. In the accesspoint 1, it is confirmed to receive ACK signal from the station 4-1 asshown in step S13. The access point 1 is maintained in the receptionmode, if no ACK signal is received. The transmission enabling section 19set the transmitter modules 12-1, 12-2, 12-3 in the transmissionenabling state, when ACK signal is received as shown in step 13. Thetransmission data are transmitted from the transmitter modules 12-2,12-3 to the station 4-2, 4-3 at the same time, after elapse of thewaiting time, as shown in step S14. The transmission data is transmittedas data packets each having same packet length. The access point 1 isswitched from the transmission mode to the reception mode after thetransmission of the data packets is finished. In the reception mode, thereceiver module can receive ACK signal from the stations 4-2, 4-3.

At the access point 1 provided with the reception end detecting section18 and the transmission enabling section 19 as shown in FIG. 2, thetransmissions from the transmitter modules 12-1 to 12-3 to the wirelessstations 4-1 to 4-3 are started at the same time in the transmissionwaiting state of the transmission mode after transfer from all thewireless stations 4-1 to 4-3 to the receiver modules 11-1 to 11-3 hasterminated. Therefore, at the access point 1, good communication betweenthe access point 1 and the wireless stations 4-1 to 4-3 each can beestablished without causing interference between transmission andreception.

Now, the adaptive array antenna shown in FIG. 2 will be described indetail with reference to FIG. 4. FIG. 4 shows a specific example ofcircuit configuration of the adaptive array antenna 2 shown in FIG. 2.

The adaptive array antenna 2, as shown in FIG. 4, comprises antennaelements 30-1 to 30-3 for receiving an RF signal, transmission/receptionchangeover switches 31-1 to 31-3 for switching one of transmission modeand reception mode, low noise amplifiers (LNAs) 32-1 to 32-3 foramplifying a received RF signal with a low noise, and down converters33-1 to 33-3 for converting a frequency bandwidth from a radio frequency(RF) of an RF signal to an intermediate frequency (IF) or base band(BB). In addition, the adaptive array antenna 2 comprises distributors34-1 to 34-3 for distributing output signals from the down converters33-1 to 33-3, and receiving beam forming circuits 35-1 to 35-3 forweighting and combining input signals distributed in accordance with areception complex weighting coefficient set by a beam control section40, and forming a reception signal corresponding to each receptionantenna beam as a result of such weighting and combining. Further, theadaptive array antenna 2 comprises transmission beam forming circuits36-1 to 36-3 for forming a transmission beam signal to form transmissionbeams by weighting the transmission signal in accordance with thetransmission complex weighting coefficient set by the beam controlsection 40, and composers 37-1 to 37-3 for composing transmission beamsfrom the transmission beam signals. Furthermore, the adaptive arrayantenna 2 comprises up converters 38-1 to 38-3 for converting anintermediate frequency (IF) or a base band into a radio frequency (RF)of an RF signal, power amplifiers 39-1 to 39-3 (hereinafter, simplyreferred to as PA) for amplifying an RF signal, and the beam controlsection 40.

The transmission/reception changeover switches 31-1 to 31-3, LNA 32-1 to32-3, down converters 33-1 to 33-3, distributors 34-1 to 34-3, composers37-1 to 3-3, up converters 38-1 to 38-3, and PAs 39-1 to 39-3 correspondto the respective antenna elements 30-1 to 30-3, and are provided to beequal to the antenna elements 30-1 to 30-3 in number (three elements inthis example). On the other hand, the receiving beam forming circuits35-1 to 35-3 and transmission beam forming circuits 36-1 to 36-3 areprovided to be equal to antenna beams formed by the adaptive antenna 2in number (three beams in this example). The number of antenna beams maybe smaller or greater than that of the antenna elements 30-1 to 30-3.

Now, an operation of the adaptive array antenna 2 shown in FIG. 4 willbe briefly described below.

At the adaptive array antenna 2, the RF signals received by the antennaelements 30-1 to 30-3 are inputted to the LNAs 32-1 to 32-3 viatransmission or reception changeover switches 31-1 to 31-3,respectively, and the inputted signals are amplified at a predeterminedlevel. The RF signals amplified by the LNAs 32-1 to 32-3 are inputted tothe down converters 33-1 to 33-3, respectively. The frequency bandwidthis converted from the radio frequency (RF) into the intermediatefrequency (IF) or base band (BB), and the converted signal is inputtedto the distributors 34-1 to 34-3.

The distributor 34-1 distributes output signals from the down converters33-1 to 33-3 to the receiving beam forming circuit 35-1. The distributor34-2 distributes output signals from the down converters 33-1 to 33-3 tothe receiving beam forming circuit 35-2. The distributor 34-3distributes output signals from the down converters 33-1 to 33-3 to thereceiving beam forming circuit 35-3.

The beam control section 40 sets a reception complex weightingcoefficient. At the receiving beam forming circuits 35-1 to 35-3, theinput signals are weighted and combined in accordance with thisreception complex weighting coefficient. As a result, a plurality ofreception antenna beams are formed. The signals corresponding to thereception antenna beams from the receiving beam forming circuits 35-1 to35-3 are supplied to the receiver modules 11-1 to 11-3 in FIG. 2,respectively.

On the other hand, transmission signal s TS1 to TS3 from the transmittermodules 12-1 to 12-3 shown in FIG. 4 are inputted to the transmissionbeam forming circuits 36-1 to 36-3, respectively. At the transmissionbeam forming circuits 36-1 to 36-3, a plurality of transmission complexweighting coefficients set by the beam control section 40 are multipliedrelevant to the respectively inputted transmission signal s.

A plurality of output signals from the transmission beam forming circuit36-1 are inputted to the composers 37-1 to 37-2. A plurality of outputsignals from the transmission beam forming circuit 36-2 are alsoinputted to the composers 37-1 to 37-3 similarly. A plurality of outputsignals from the transmission beam forming circuit 36-3 are alsoinputted to the composers 37-1 to 37-3 similarly. At the composers 37-1to 37-3, a plurality of signals inputted respectively are composed intoone signal.

The output signals from the composers 37-1 to 37-3 are inputted to theup converters 38-1 to 38-3, respectively. The frequency bandwidth isconverted from the intermediate frequency (IF) or base band (BB) intothe radio frequency (RF), and then, the converted signal is inputted tothe PAs 39-1 to 39-3. The transmission signal s amplified by the PAs39-1 to 39-3 are supplied to the antenna elements 30-1 to 30-3respectively via the switches 31-1 to 31-3, and the supplied signals aretransmitted to the stations.

At the beam control section 40, as described previously, a receptioncomplex weighting coefficient is set at the receiving beam formingcircuits 35-1 to 35-3 each, and a transmission complex weightingcoefficient is set at the transmission beam forming circuits 36-1 to36-3 each. During transmission and reception, a weighting coefficientfor communicating with the same station is set at the mutuallycorresponding beam forming circuits, for example, the receiving beamforming circuit 35-1 and the transmission beam forming circuit 36-3.

Now, the reception end detecting section 18 shown in FIG. 2 will bedescribed in detail with reference to FIG. 5.

FIG. 5 is a block diagram showing the reception end detecting section 18shown in FIG. 2. As shown in FIG. 5, the reception end detecting section18 comprises detecting sections 20-1, 20-2, and 20-3 in which a headerof a data packet included in reception signals from the receiver modules11-1 to 11-3 each is inputted and which detect a reception end time fromtime information from the header, a detecting section 21 for detecting amaximum value of the reception end time detected by the detectingsections 20-1, 20-2, and 20-3 each, and a notifying section 22 notifyingthat the maximum value of this reception end time is set, and receptionterminates when the maximum reception end time is counted by a counter23.

The reception signal inputted to the receiver modules 11-1 to 11-3 eachincludes a data packet, and this data packet has a data structure asshown in FIG. 6 as an example. This data packet comprises a transmissiondestination for specifying the receiver modules 11-1 to 11-3, atransmission source for specifying the wireless stations 4-1 to 4-3, apacket header having described therein a predetermined time periodrequired from the start of reception of this data packet to the end ofsuch reception, and packet data having stored therein content data suchas video image, voice, text, or program.

When a packet is inputted to the receiver modules 11-1 to 11-3 each, inthe reception mode, the reception start time of the packet isestablished at a clock (not shown), and the predetermined time period inthe packet header is isolated from the packet. The required time andpacket reception start time TS are sent to the detecting sections 20-1,20-2, and 20-3, respectively. At these detecting sections 20-1, 20-2,and 20-3, the predetermined time periods Tr1, Tr2, and Tr3 (for example,Tr1<Tr2<Tr3) are added to the packet reception start time TS, and times(TrS+Tr1, TrS+Tr2, TrS+Tr3) required for the completion of this packetreception are obtained. These reception completion times (TrS+Ts1,TrS+Tr2, TrS+Tr3) are provided to the detecting section 21. At thedetecting section 21, the reception completion times (TrS+Tr1, TrS+Tr2,TrS+Tr3) are compared with each other, and the maximum time of thesereception completion times (TrS+Tr1, TrS+Tr2, TrS+Tr3), for example, themaximum time (TrS+Tr3) is obtained. This time (TrS+Tr3) is set at thereception end notifying section 22, and a timer 23 monitors this time(TrS+Tr3). A timer 14 is composed of a digital counter, for example, anda current time TC is clocked. At the reception end notifying section 22,when the time being monitored reaches the maximum time (TrS+Tr3), thereception end signal is provided from the notifying section 22 to atransmission enabling section 19. This transmission enabling section 19provides a transmission enable signal to each of the transmitter modules(12-1, 12-2, 12-3) in response to the reception end signal, changes acurrent state from a transmission disable state to a transmission enablestate, and enables transmission. That is, the access point 1 is changedin the transmission mode from the reception mode in response to thereception end signal.

A packet structure shown in FIG. 6 is provided as an example, and may beanother structure. For example, as shown in FIG. 7, a description of apredetermined time period ‘Tx’ may not be given at the packet header,and a transmission rate and a packet data size may be described insteadof the description of the predetermined time period. In this packet asshown in FIG. 7, the time period ‘Tx’ required for packet transfer isobtained from the description of the transmission rate and data size.That is, at the detecting sections 20-1, 20-2, and 20-3, the describeddata size is divided at the transmission rate, whereby the time period‘Tx’ required to transmit that packet can be obtained.

The transmission enabling section 19 shown in FIG. 2 will be describedwith reference to FIG. 8.

FIG. 8 shows a circuit block of the transmission enabling section 19shown in FIG. 2. This transmission enabling section 19 comprises asetting section 15 for setting transmission at a waiting state. When thecurrent time Tc clocked by the timer 14 reaches the maximum time Tt3 atwhich the end of transmission is predetermined, this setting section 15sets a transmission waiting state in the transmission mode, in whichtransmission to the transmission enabling section 19 is waited. Forexample, the setting section 15 sets a flag, i.e., a start flag forcomputing a time period in which transmission is waited, at a computingsection 16 for computing a time period at which transmission is waited.The transmitter modules 12-1 to 12-3 and the computing section 16 forcomputing a transmission waiting time is controlled by a firsttransmission control section 17.

When there exists packet data to be transmitted from the access point 1to at least one of the wireless stations 4-1 to 4-3, the firsttransmission control section 17 specifies at least one transmittermodule for transmitting the packet data from among the transmittermodules 12-1 to 12-3, specifies an address (hereinafter, referred to asdestination or transmission destination address) of a destinationstation, i.e., a target station to which data is to be transmitted forthe thus specified transmitter module, and specifies data to betransmitted. At the same time as this specification, the firsttransmission control section 17 sets a flag, i.e., an enable flag forenabling computation of the transmission wait time, at the computingsection 16 for computing a transmission waiting time period.Transmission data specified for the transmitter modules 12-1 to 12-3 bythe first transmission control section 17 does not correspond tooriginal data, and corresponds to data to be transmitted in a wirelessinterval, i.e., modulated data and error corrected data. Thistransmission data has a data packet structure in which a packet headeris provided to the packet data as shown in FIG. 6 or FIG. 7. To thepacket data, there is provided address information such as transmissionsource corresponding to a transmission destination address of the accesspoint or a transmission destination specified by a destination address,and time information or the like required for transfer of transmissiondata.

When an enable flag is set by the first transmission control section 17,and a start flag for starting a transmission wait is set by thetransmission waiting state setting section 15, a time period in which atransmission waiting state is maintained from a time at which atransmission waiting state is set, i.e., a transmission wait time periodis computed in random by the computing section 16. When a time periodfor this transmission wait has elapsed, a transmission instruction isprovided from the computing section 16 to a transmitter module to whichdata is to be transmitted, of the transmitter modules 12-1 to 12-3.Then, the set data is transmitted to a wireless station of the setdestination address via the adaptive array antenna 2.

After one or a plurality of transmitter modules 12-1, 12-2, and 12-3start(s) transmission at the same time after the elapse of the wait timeperiod, if a length of a packet to be transmitted is constant,transmission is terminated at the same time.

A more detailed circuit block diagram for providing the reception enddetecting section 18 shown in FIG. 5 and showing the reception enddetecting section 18 adaptive to the circuit shown in FIG. 8, will bedescribed with reference to FIG. 9.

The reception end detecting section 18 shown in FIG. 9 is composed ofreception start detectors 41-1 to 41-3 for detecting a receptionstarting time, and reception reservation detectors 42-1 to 42-3 fordetecting a time period reserved for reception. The detecting section 18further comprises adders 43-1 to 43-3 for adding a reception reservationperiod to the reception start time, thereby obtaining the predeterminedtime at which reception is terminated, a selecting section 44 forselecting a maximum value from a plurality of reception end times, astorage section 45 for storing the maximum value of the selectedreception end time, and an update section 46 for updating a maximumreception end time.

Now, an operation of the detecting section 13 for detecting the maximumreception end time shown in FIG. 9 will be described here.

At the detectors 41-1 to 41-3 for detecting a reception start time, atransmission start time of a station being a transmission source isdetected from the reception signals RS1 to RS3. This transmission starttime is detected as a time at which a first packet of the receptionsignals RS1 to RS3 each is detected, i.e., a time at which the wirelessstations 4-1 to 4-3 being transmission sources transmit the packet.

At the detectors 42-1 to 42-3 for detecting a reception reservation timeperiod, a transmission reservation time period corresponding to a timeperiod for the stations 4-1 to 4-3 each being a transmission source toreserve a communication channel for the purpose of transmission isdetected from the packet header of the reception signals RS1 to RS3each.

At the adders 43-1 to 43-3, the reception start time and receptionreservation time period detected from the reception signals RS1 to RS3respectively are added, whereby the reception end time of the receptionsignals RS1 to RS3 each is computed.

The selecting section 44 selects the maximum reception end time that isthe latest reception end time on the time-by-time base, of the receptionend times of the reception signals RS1 to RS3 obtained by the adders43-1 to 43-3. Information on the selected maximum reception end time isprovided to the storage section 45 and the update section 46. Themaximum reception end time is stored in the maximum reception end timestorage section 45.

At the maximum reception end time update section 46, when the maximumreception end time selected by the selecting section 44 is greater thanthe maximum reception end time stored in the storage section 45, thecontents of the storage section 45 are updated in accordance with themaximum reception end time selected by the selecting section 44.

That is, when the maximum reception end time selected by the selectingsection 44 is greater than the maximum reception end time stored in themaximum reception end time storage section 45, the update section 46sets a write flag at the maximum reception end time selecting section44. In this manner, a predetermined end time newly selected at thepredetermined maximum end time selecting section 44 is written in themaximum reception end time storage section 45.

The information on the maximum reception end time thus stored in thestorage section 45 is outputted from the maximum reception end timedetecting section 14. Then, the outputted information is inputted to thetransmission waiting state setting section 15 shown in FIG. 8.

The subsequent operation is as described previously. When the maximumreception end time detected by the detecting section 14 and stored inthe storage section 45 matches the current time clocked by the timer 14,the reception waiting state is set by the setting section 15. When thereception waiting state is set, the computing section 16 computes arandom transmission wait time. After the elapse of this transmissionwait time, transmission is instructed simultaneously to the transmittermodules 12-1 to 12-3. That is, back-off processing is carried out forall the transmission modules 12-1 to 12-3.

In this manner, to the stations 4-1 to 4-3 of destination addresses setat the transmission modules 12-1 to 12-3 by the first transmissioncontrol section 17, packets of data set at the transmitter modules 12-1to 12-3 are transmitted via the adaptive array antenna 2 at the sametime.

FIG. 10 shows the above-described exemplary operation. “ts1” to “ts3”denote the reception start times of the reception signals RS1 to RS3,Trs1 to Trs3 denote the reception reservation times of the receptionsignals RS1 to RS3, and “te1” to “te3” denote the reception end times ofthe reception signals RS1 to RS3, provided that te1=ts1+Trs1,te2=ts2+Trs2, and te3=ts3+Trs3. In this example, the reception end time“te2” denotes the predetermined maximum end time “temax”. After theelapse of a reception wait time “Twait” from “temax”, transmissions fromthe transmitter modules 12-1 to 12-3 are started simultaneously.

In this manner, according to the present embodiment, back-off processingis used in common by the transmitter modules 12-1 to 12-3, and packettransmissions to the stations 4-1 to 4-3 are carried out at the sametime, thus making it possible to prevent collision between transmissionand reception in the access point 1. Therefore, the back-off processingis effective in communication in which a reception acknowledge is notmade by an ACK (acknowledge response) packet, for example, in increasingthe success rate of a broadcast, for example.

On the other hand, in a method in which the stations 4-1 to 4-3transmits an ACK packet and executes a reception acknowledge when theyreceives transmission packets from the access point 1, it is desirablethat the first transmission control section 17 for controllingtransmission to the access point 1 be equal to a size (time length) ofdata to be set at the transmitter modules 14-1 to 12-2.

By doing this, ACK packet transmissions from the stations 4-1 to 4-3occur at the same time. Thus, ACK packet transmitted by one station canbe prevented from interfering with another station. Therefore, thecompletion of data packet reception is acknowledged in accordance withthe ACK packet. This method is effective in transmission other thanbroadcast transmission. Of course, when the same data is transmitted toa plurality of stations as in broadcast transmission, ACK packetreception is acknowledged. As a result, the reliability can be improved.

From the transmitter modules 12-1 and 12-2, simultaneous transmission tothe stations 4-1 and 4-3 is started respectively via the antenna beams3-1 and 3-2. Then, where transmission to one station, for example, thestation 4-1, first terminates, and where there exists a station at whichtransmission does not terminate, for example, the station 4-2, a datapacket may be transmitted to the station 4-2 by the transmitter module12-1 for use in transmission to the station 4-1 at which transmissionterminates, via the antenna beam 3-1 for use in transmission to thestation 4-1. By doing this, the station 4-1 carries out carrier sensingand enters a back-off period. Thus, the station 4-1 can be preventedfrom transmitting a signal, which interferes with another station. Suchcontrol is carried out by the first transmission control section 17.

Further, after simultaneous transmissions are started from thetransmitter modules 12-1 and 12-2 to the stations 4-1 and 4-3 via theantenna beams 3-1 and 3-2, respectively, where transmission to onestation, for example, the station 4-1 first terminates, and there existsa station at which transmission does not terminate, for example, thestation 4-2, a directivity pattern of the antenna beam 3-2 may bechanged so that transmission antenna beam corresponding to the station4-2, for example, the antenna beam 3-2 has a directivity gain in thedirection of the station 4-2. Even by doing this, the station 4-1carries out carrier sensing and enters the back-off period. Thus, thestation 4-1 can be prevented from transmitting a signal, whichinterferes with another station.

An access point 1 in a wireless communication system according to asecond embodiment of the present invention will be described withreference to FIG. 11.

At the access point 1 shown in FIG. 11, detectors 21-1 to 21-3 fordetecting an acknowledge response (ACK), address comparators 22-1 to22-3, and retransmission data storage sections 25-1 to 25-3 are added tothe access point 1 shown in FIG. 8. Further, a second transmissioncontrol section 24 is provided instead of the first transmission controlsection 17 shown in FIG. 8.

The second transmission control section 24 has a function for outputtingto the retransmission data storage sections 25-1 to 25-3 the destinationaddresses to be set to the transmitter modules 12-1 to 12-3 and data tobe retransmitted, in addition to a function of the first transmissioncontrol section 17. The destination address and retransmission datastored in the retransmission data storage sections 25-1 to 25-3 are usedduring data retransmission. Further, the destination addresses to be setat the transmitter modules 12-1 to 12-3 are outputted to addresscomparators 22-1 to 22-3 as well. The transmission data is supplied tothe corresponding transmitter module 12-1 to 12-3 and is also suppliedto the retransmission data storage sections 25-1 to 25-3 under thecontrol of the second transmission control section 24 from the datasupply section 10 so that the retransmission data is stored in thestorage sections 25-1 to 25-3

Acknowledge response signals (ACK packets) are transmitted from thestations 4-1 to 4-3 to the receiver modules 11-1 to 11-3, respectivelyand received at the receiver modules 11-1 to 11-3. This receivedacknowledge response signals are inputted to the detectors 21-1 to 21-3,and are detected, respectively. At the acknowledge response detectors21-1 to 21-3, station addresses (transmission address) which denotes theACK packet transmission source or station is detected from the ACKpackets inputted respectively, and these addresses are outputted to theaddress comparators 22-1 to 22-3, respectively.

The address comparators 22-1 to 22-3 compare the destination addressoutputted from the second transmission control section 24 with thetransmission source addresses inputted from the acknowledge responsedetectors 21-1 to 21-3 respectively, and detectsconsistency/inconsistency of these addresses. Where consistency isobtained, an address consistency flag is set at the second transmissioncontrol section 24.

The second transmission control section 24 checks whether or not theaddress consistency flag is set at the address comparators 22-1 and 22-2after a predetermined time clocked by the timer 14 at a time when a datapacket is transmitted from the transmitter modules 12-1 to 12-3. As aresult, where the address consistency flag is not set at least at one ofthe address comparators 22-1 and 22-2, i.e., where the destinationaddress and transmission source address are inconsistent at least at oneof the address comparators 22-1 and 22-2, the second transmissioncontrol section 24 resets the destination address and data stored in theretransmission data storage sections 25-1 to 25-3 at the transmittermodules 12-1 to 12-3. In addition, this control section sets an enableflag for enabling computation of a transmission wait time at thecomputing section 16 for computing the transmission wait time.

When a random transmission wait time is thus computed at thetransmission wait time computing section 16, and this transmission waittime elapses, transmissions are instructed simultaneously from thesecond transmission control section 24 to the transmitter modules 12-1to 12-3. Then, data packets are retransmitted at the same time from thetransmitter modules 12-1 to 12-3 to the stations 4-1 to 4-3 via theadaptive array antenna 2.

As has been described, according to the present embodiment, it isdetermined that the ACK packets are received from the plurality ofstations 4-1 to 4-3 at the same time. Further, back-off processing iscarried out in common at the transmitter modules 12-1 to 12-3, andpackets are retransmitted to the stations 4-1 to 4-3 at the same time.Therefore, even during packet retransmission, the collision betweentransmission and reception at the access point 1 can be prevented.

In the foregoing description, where the destination address andtransmission source address are inconsistent at least at one of theaddress comparators 22-1 and 22-2, in other words, even where only onestation does not transmit an ACK packet, packets are retransmitted toall the stations 4-1 to 4-3. However, a packet may be retransmitted toonly a station, which does not transmit an ACK packet, and a new datapacket may be transmitted to a station, which has transmitted such ACKpacket, whereby the performance of the entire system can be improved.

Where a predetermined number or more is obtained after counting thenumber of retransmissions, packet retransmission to a station, whichdoes not transmit an ACK packet, is canceled, whereby the performance ofthe entire system can be prevented from being lowered by a specificstation whose reception state is poor.

A transmitter module deactivated by cancellation of packetretransmission, or alternatively, a transmission module deactivated bythe end of normal transmission, is assigned to transmission to anotherstation, whereby the performance of the entire system can be improved.Further, combination with a physical carrier sense can be obtained.

These controls are executed by the second transmission control section24.

A wireless communication system according to a third embodiment of thepresent invention will be described with reference to FIG. 12.

The access point 1 shown in FIG. 12 comprises a array antenna 2 capableof dividing a space in accordance with a plurality of antenna beams,beam forming circuits 51-1 to 51-M for forming M antenna beams, and abeam selecting section 52 for selecting one of the antenna beams formedby the beam forming circuits 51-1 to 51-M. Further, the access point 1comprises a packet length determining section 53 for determining apacket length of a reception signal, a control packet generating section54 for generating a control packet for causing another station torecognize the predetermined maximum end time of a station whentransmission has been carried out from the access point 1, and a controlsection 55. The control packet generated from the control packetgenerating section 54 includes a frame control for designating that thispacket is a control packet, a duration required for transmitting thedata packet, a receiver address for designating the station to which thecontrol packet will be transmitted, and a frame check sequence forchecking errors of the data packet.

On the other hand, stations 4-1 to 4-N has such a configuration as tocommunicate with only the access point 1 without receiving a signaltransmitted from another station. These stations each comprise a controlsection 60, a control packet determining section 61 for determining thecontents of control packets transmitted from the access point 1, atransmission timing deciding section 62 for deciding a transmissiontiming of a signal, i.e. a packet, to be transmitted by the station, apacket length determining section 63 for determining a packet length ofa reception signal from the access point 1, a transmitting/receivingsection 64, and an antenna 65.

The wireless communication system shown in FIG. 12 is operated as shownin FIG. 14.

When a transmission request occurs, if a control packet shown in FIG. 12or a data packet transmitted from the access point 1 is not received,the station 4-1 sets at the transmitting/receiving section 64 the datato be transmitted by the control section 60. When the transmitting ofthe data packet is prepared, a RTS (request to set) packet istransmitted to the access point 1 from the transmitting/receivingsection 64 of the station 4-1, as shown in step S30 of FIG. 14. Theaccess point 1 waits for a time duration td1 from the reception of theRTS packet to transmit CTS (clear to sent) packet to the station 4-1, asshown in step S31. The packet of data stored in thetransmitting/receiving section 64 is transmitted as an electricmagneticwave from the antenna 65, as shown in step S32, after the station 4-1receives CTS packet, as shown in step S32.

At the access point 1, the adaptive array antenna 2 receives theelectric-magnetic wave transmitted from the station 4-1, and a receptionsignal is inputted to the beam selecting section 52 via the beam formingcircuits 51-1 to 51-M. At the beam selecting section 52, one of thereception signals from the beam forming circuits 51-1 to 51-M isselected. The selected reception signal is inputted to the controlsection 55.

The packet length-determining section 53 determines a packet length ofthe reception signal inputted to the control section 55. Based on thisjudgment, the station 4-1 sends, to the control packet generatingsection 54, information on the packet length of a control packet to benext transmitted. The control packet-generating section 54 generates acontrol packet of a packet length provided by the packetlength-determining section 53, and sends the packet to the controlsection 55.

When the control section 55 of the access point 1 has successfullyreceived a signal transmitted from the station 4-1, if a receptionsignal packet is a transmission request (RTS: Request To Send) packet, atransmission clear (CTS: Clear To Send) packet is sent to thetransmitting/receiving section 64 of the station 4-1 via the antennabeams formed by the array antenna 2 and the beam forming circuit, whichreceives the RTS packet or the ACK packet, as shown in step S31 of FIG.14. Alternatively, if the reception signal packet is a data packet, anACK packet is also sent to the transmitting/receiving section 64 of thestation 4-1 via the antenna beams formed by the array antenna 2 and thebeam forming circuit, which receives the RTS packet or the ACK packet,as shown in step S33 of FIG. 14. The control section 55 transmits a CTSpacket or ACK packet via an antenna pattern for use in reception. Whenthe control section 55 forms an antenna beam other than the antenna beamfor use in reception, the control section 55 transmits a control packetwhich is generated in the control packet-generating section 54.

Of the packets thus transmitted from the access point 1, the CTS packetor ACK packet is received at the station 4-1, and the control packetshown in FIG. 13 is received at other stations 4-2 to 4-N.

The other station 4-2 to 4-N receives the control packet from the accesspoint 1, as shown in step 34 of FIG. 14, when the CTS packet is set tothe station 4-1 from the access point, as shown in step 34 of FIG. 14.If the other station 4-2 is prepared to transmit data packet to be sentto the access point 1, transmission timing is determined after an elapseof a time duration td2, based on the control packet and the data packet.Thus, the data packet is transmitted, at the transmission timing, fromthe station 4-2 to 4-N to the access point 1, as shown in step S35 ofFIG. 14.

When the access point 1 can successfully receives the data packets fromthe stations 4-1 to 4-2, the access point 1 waits for a time durationtd1 to sent ACK packet to the station 4-1, 4-2, as shown in steps 33,S36 of FIG. 14. Thus, the successive operational procedures arefinished.

Now, procedures for transmitting/receiving a packet between the accesspoint 1 and the wireless stations 4-1 to 4-N shown in FIG. 12 will bedescribed in detail with reference to FIGS. 15A, 15B, 16A, 16B, 16C and17.

The access point 1, for example, as shown in FIG. 15A, is locatedbetween the stations 4-1 and 4-2 and receives a signal transmitted fromthe station 4-1 in an up-link. As shown in FIG. 15B, in a down-link, anantenna beam 81 is formed in the direction of the station 4-1, and anantenna beam 82 is formed in the direction including that of the otherstation 4-2. The beam forming circuits 51-1 to 51-M form these antennabeams 81 and 82.

FIG. 16A to FIG. 16C are a timing chart showing a transmitting/receivingoperation of the station 4-1, access point 1, and station 4-2, and FIG.17 shows operational procedures in the station 4-1. As shown in FIG. 16Ato FIG. 16C, before the station 4-1 transmits a data packet, a RTS(Request To Send) packet 91 is transmitted from the station 4-1 to theaccess point 1, the access point 1 having received the RTS packet 91transmits a CTS (Clear To Send) packet 92 to the station 4-1, and thestation 4-1 having received the CTS packet 92 transmits a data packet93. Information on a transmission reservation time is contained in theRTS packet 91. In accordance with this RTS packet 91, the access point 1can know a maximum end time of ending transfer of a data packet from thestation 4-1.

In addition, the access point 1 transmits the CTS packet 91 and ACKpacket 96 generated by the control section 55 to the station 4-1 byusing an antenna beam 81 of FIG. 15B oriented to the direction of thestation 4-1. Further, the access point 1 transmits a control packet 94,as shown in FIG. 13, which is generated by the control packet generatingsection 54, to the station 4-2 by using an antenna beam 82 that coversthe direction of the station 4-2. Information on a transmission end time“te1” or the time duration, which is obtained from the transmissionreservation time contained in the RTS packet 91 transmitted from thestation 4-1 is contained in this control packet 94.

Where another station 4-2 has a data packet to be transmitted to theaccess point 1, the station 4-2 decides a transmission timing of thatdata packet based on analysis of the control packet 94 transmitted fromthe access point 1. That is, the control packet 94 is inputted to acontrol packet-determining section 61. From this controlpacket-determining section 61, the predetermined transmission end time“te1” is outputted as the judgment result to a transmission timingdeciding section 62. The transmission timing deciding section 62 decidesa transmission timing of the data packet 95 to be transmitted next sothat the predetermined transmission end time “te2” is identical to thepredetermined transmission end time “te1” of the data packet 93transmitted from the station 4-1. Alternatively, the access point 1transmits the data packet 95 at transmission timing free of beingoverlapped with a transmission time of the ACK packet 96 relevant to thedata packet 93 from the station 4-1 while the data packet 95 is receivedfrom the station 4-2.

In the other station 4-2, when the transmitting/receiving section 64receives a packet as shown step 20 of FIG. 18, the packet is supplied tothe control section 60 as shown in step 20 of FIG. 17 and the controlpacket determining section 61 determines whether or not the packet is acontrol packet. If the received packet is not the control packet, nodata packet is transmitted from the station to the access point 1 (stepsS41 and S42 of FIG. 18). If the received packet is control packet,packet information in the control packet is supplied to the controlpacket determining section 61 as shown in step S21 of FIG. 17. In thecontrol packet-determining section 61, a transmission end time isdetermined in accordance with the time duration in the control packet,as shown in step S43 of FIG. 18. The determined transmission end time issupplied to the transmission timing determining section 62, as shown instep S20 of FIG. 17. The information concerning a data packet to betransmitted is supplied to the packet length determining section 63 fromthe control section 60, as shown in step S23 of FIG. 17. In the packetlength-determining section 63, a time period for transmitting the datapacket is calculated, as shown in S43 of FIG. 18. The calculated timeduration is supplied to the transmission timing determining section 64as shown S24 of FIG. 17. In the transmission timing determining section64, it is determined whether or not the data packet has the packetlength which can finish the transmission of the data packet at thetiming of the transmission end time, as shown in step 44 of FIG. 18. Ifthe data packet cannot be transmitted before the transmission end time,the transmission of the data packet is inhibited, as shown in step S42of FIG. 18. If the data packet can be transmitted before thetransmission end time, the transmitting timing determining section 64 sodetermines a star timing of transmitting the data packet as to end thetransmission of the data packet at the transmission end time, as shownin step of FIG. 18. The star timing is supplied to the control section60 as shown in step S25 of FIG. 17 and the control section 60 causes thetransmitting/receiving section 64 to start the transmission of the datapacket at the start timing. Thus, the data packet is transmitted fromthe station 4-2 to the access point section 1, as shown in step S46 ofFIG. 18.

In this way, the access point 1 does not receive the data packet 95 fromthe station 4-2 during transmission of the ACK packet 96, thus enablingSDMA. Where the access point uses a CSMA method, it is difficult for theaccess point to carry out transmission and receiving at the same time,since a transmission signal interferes with a reception signal. However,in the present embodiment, there is an advantage that the access point 1can carry out SDMA without carrying out transmission and receiving atthe same time.

A station having received a control packet does not transmit a datapacket if a transmission request exists. At this time, the access point1 can transmit an ACK packet 97 at a timing of transmitting the ACKpacket 96, as shown in FIG. 16B.

A circuit configuration of the station 4-i (i=1, 2, . . . N) in a fourthembodiment of the present invention will be described with reference toFIG. 19.

As shown in FIG. 19, at the station 4-i, a random probability generatingsection 66 is added to the station 4-i shown in FIG. 11. As shown inFIG. 14, at the station 4-i, a control packet determining section 61 hasa function for determining whether or not a control packet transmittedfrom the access point 1 has a broadcast address in which all thestations 4-i are a transmission destination. A random probabilitygenerating section 66 generates a random probability, for example, arandom probability of a value between 0 and 1, and provides theprobability to a transmission timing deciding section 62.

Now, an operation of a wireless communication system comprising astation shown in FIG. 19 will be described by focusing on a differencefrom a wireless communication system shown in FIG. 11.

At the station 4-i, a reception signal from an antenna 65 is inputted toa transmitting/receiving section 64. A packet of this receiving signalis inputted via a control section 60, or alternatively, directly to acontrol packet determining section 61. On the other hand, when thecontrol section 60 delivers an RTS packet to the transmitting/receivingsection 64, a packet length-determining section 63 determines a packetlength of that RTS packet.

When it is determined by the control packet determining section that thecontrol packet has a broadcast address at the control packet determiningsection 61, a packet transmission timing is decided in random at thetransmission timing deciding section 62 in accordance with a randomprobability generated at the random probability generating section 66. Adata packet is inputted from the control section 60 to thetransmitting/receiving section 64 at this randomly decided transmissiontiming and transmitted by the antenna 65.

When there are a plurality of stations 4-i communicating with the accesspoint 1 in an infrastructure mode, a plurality of stations 4-i receivesa control packet transmitted from the access point 1. Therefore, whenthe access point 1 selects a destination address of one station fromwhich a control packet is to be transmitted, from among the addresses ofa plurality of stations 4-i, the station having received the controlpacket can transmit a data packet without collision with a data packettransmitted from another station.

Where a transmission request does not exist, the station having receivedthe control packet transmitted from the access point 1 does not transmita data packet. Thus, the access point 1 transmits a control packet withanother station being a destination address. However, when a largenumber of stations 4-i exists and a small number of transmissionrequests of individual stations exists, processing becomes complicatedin a method of thus changing the destination address of station, therebytransmitting the control packet.

In contrast, in the present embodiment, when a control packet istransmitted from the access point 1, such a control packets istransmitted to all the stations 4-i with the destination address being abroadcast. In this manner, while the access point 1 eliminates aninconvenience of changing the destination address of the control packet,a station having a transmission request can transmit a data packetimmediately.

In this case, a plurality of stations 4-i have a transmission privilege,each packet is transmitted at timing in accordance with the randomprobability generated by the random probability generating section 66.In this manner, even if a plurality of stations 4-i are in atransmission request state, it is possible to reduce the probability ofcollision of packets transmitted by the stations each.

According to the wireless communication system according to the first tofourth embodiments described above, the access point can carry outproper transmitting/receiving between a plurality of stations while theSDMA method is applied to the CSMA method.

A wireless communication system according to the fifth to ninthembodiments of the present invention will be described with reference toFIG. 20 to FIG. 27.

In the wireless communication system according to the fifth embodimentshown in FIG. 20, a CSMA/CA (Carrier Sense Multiple Access CollisionAvoidance) protocol is applied.

As shown in FIG. 20, a wireless access point 101 connected to a wirednetwork or the like comprises wireless module sections 102-1 and 102-2for transmitting/receiving a radio signal. There are wireless stations104-1 to 104-m for determining the possibility of one or a plurality ofmutually autonomous transmissions using the same channel as the wirelessmodule section 102-1 and determining the possibility of one or aplurality of mutually autonomous transmissions using the same channel asthe wireless stations 103-1 to 103-n and wireless module section 102-2under the SCM/CA method for avoiding collision of wireless packets, thewireless stations being controlled under the CSMA/CA (Carrier SenseMultiple Access Collision Avoidance) protocol for avoiding collision ofwireless packets.

In the system shown in FIG. 20, the wireless module section 102-2receives a signal transmitted from the wireless module section 102-1,even if a different channel exists. In addition, the section 102-1receives a signal transmitted from the section 102-2 as well.

A description will be given with respect to a wireless communicationsystem according to the fifth embodiment of the present invention foravoiding a packet error caused by interference of bypassing of atransmission signal between wireless communication modules targeted forsuch a wireless communication system.

FIG. 21 is a block diagram showing a wireless access point 101 accordingto the fifth embodiment of the present invention. In FIG. 21, thewireless module 102-1 has a transmitting/receiving antenna 201, atransmitting/receiving section 202, a reception information notifyingsection 203, and a wireless module control section 204. The wirelessmodule 102-2 has a transmitting/receiving antenna 205, atransmitting/receiving section 206, a reception information acquiringsection 207, and a wireless module control section 208.

At the wireless access point 101 shown in FIG. 21, a radio signalreceived by the transmitting/receiving antenna 201 is modulated by thetransmitting/receiving section 202, and the modulated signal is inputtedas data to the wireless module control section 204. The wireless modulecontrol section 204 transmits, to the reception information notifyingsection 203, information on a reception period of data being received ora data reception end time. The reception information-notifying section203 transmits the information to the reception signal acquiring section207 of the wireless module 102-2. The reception signal acquiring section207 notifies the wireless module control section 208 that the wirelessmodule 102-1 is being received. The wireless module control section 208controls the transmitting/receiving section 206 so that thetransmitting/receiving antenna 205 of the wireless module 102-2 does notoutput a radio signal.

Thus, if the wireless module section 102-2 use a different channel asthat of the wireless module section 102-1 or have a directivity antennaswhich use a same channel as that of the wireless module 102-1, thewireless module sections 102-2 is so controlled as to transmit no radiosignal, in a state that the wireless module section 102-2 communicateswith the corresponding station 104-1 to 104-m via the channel.Therefore, in the radio signal being received by the wireless module102-1, it is possible to reduce an error of the reception of the radiosignal, since a transmission signal of the wireless module 102-1 is notoutputted as an interference signal.

Even where the wireless module 102-1 and wireless module 102-2 use theadjacent frequency bandwidth, a mutually transmitting signal has adifferent frequency. A radio signal outputted by the wireless module102-1 is received without being restricted by a filter. The wirelessmodule transmits a signal with a large amount of power. Thus, if themodule is installed at the same casing or in its neighboring place, evenif the mutual wireless communication modules have the differentfrequency, interference occurs.

Thus, it is required that the wireless module section operates incorporation with the mutual transmitting/receiving timing.

An operation of wireless communication modules 102-1 and 102-2 in thewireless communication system according to the sixth embodiment of thepresent invention will be described with reference to FIG. 22.

In FIG. 22, the wireless module section 102-1 transmits ACK packets301-0 to 301-2 and receives data packets 302-0 to 302-3. The wirelessmodule section 102-2 transmits a synchronizing packet 303-0 and ACKpackets 304-0 and 304-1 and receives data packets 305-0 and 305-1.

When a wireless module 102-1 receives the data packet 302-0, ittransmits to the wireless module 102-2 the fact that the data packet isbeing received. In addition, the packet time length and packet receptionend time of the simultaneously received data packet 302-0 as well arenotified to the element 102-2. That is, in response to the reception ofthe data packet, the control section 204 informs to the receptioninformation-acquiring section 207 via the receptioninformation-notifying section 203, the reception of the data packet atthe wireless module 102-1, a packet time length of the data packet302-0, and a packet reception time. The wireless module 102-1 transmitsACK packet 301-0 to the station 103-1 to 103-3, when the wireless module102-1 have received the data packet. The wireless module 102-2 transmitsa synchronizing packet at the same time length as the ACK packet 301-0in synchronized with the transmission timing of the ACK packet 301-0.

The wireless module predicts the transmission timing of the ACK packetfrom the packet time length and the packet reception end time of thedata packet 302-0, which is acquired by the reception informationacquiring section 207, and the control section 208 causes thetransmitting/receiving section 206 to transmit the synchronizing packetto the station 104-1 to 104-m at the transmission timing. Thetransmission end time information is contained in the synchronizingpacket, and the wireless station using the same channel as the wirelessmodule 102-2 can know a time at which transmission is to be terminatedin the wireless station 104-1 to 104-m. The wireless station 104-1 to104-m receives the synchronizing packet 303-0. Where a data packet to betransmitted exists, the wireless station 104-1 to 104-m decides the timelength and transmission time of the data packet and so transmits thedata packet as to terminates at the transmission end time notified bythe synchronizing packet 303-0.

Where fragmented data packets are consecutively received at the wirelessmodule 102-1, the wireless station 104-1 to 104-m using the same channelas the wireless module 102-2 as well divides a data into segment datawhich is packed in the data packet with the packet time length notifiedby the synchronizing packet 303-0 to transmit the data packet to thewireless module 102-2. Therefore, transmission and reception are carriedout by the wireless module 102-1 and wireless module 102-2 at the sametime. In this embodiment according to the present invention, the datapackets 301-0 to 301-2 and 302-0 to 302-2 have a same packet time lengthand are transmitted during the same period. In this embodiment, the datapackets 301-0 to 301-2 and 302-0 to 302-2 may have time informationrelating to the transmission time duration therein, as shown in FIGS. 5and 6, and the packet time length and the packet reception end time maybe obtained from the time information of the transmission time duration.

As has been described above, in a wireless LAN under the CSMA/CA methodthat is a distribution control, wireless communication modules providinginterference each other can be used, making it possible to efficientlyutilize a radio frequency. This makes it possible to provide the abovechannel using the wireless module as an adjacent channel.

In addition, even where the frequency channels used by the wirelesscommunication modules are identical to each other and each wirelessmodule uses an antenna having its different directivity, oralternatively, uses an adaptive array or smart antenna capable of freelychanging directivity, a synchronizing packet is effective, making itpossible to avoid a packet transmission error due to antenna bypassing.

An operation of wireless module sections 102-1 and 102-2 in the wirelesscommunication system according to the sixth embodiment of the presentinvention will be described with reference to FIG. 23.

The wireless module 102-1 transmits a synchronizing packet 401-0, andreceives a data packet 402-0 transmitted from a wireless station 103-1to 103-m using the same channel as the module 102-1. The wireless module102-1 transmits an ACK packet 401-1 in response to a reception of thedata packet 402-0. The wireless module 102-2 also transmits thesynchronizing packet 403-0, and receives a data packet 404-0 from thewireless station using the same channel as the module 102-2. Thewireless module 102-2 also transmits an ACK packet 403-1 in response toa reception of the data packet 404-0.

The wireless module 102-1 and wireless module 102-2 transmitsynchronizing packets, respectively when no data packet is received. Thewireless stations 103-1 to 103-m having received the synchronizingpacket transmits a data packet so as to terminate transmission at atransmission end time which is decided in accordance with timeinformation in the synchronizing packet.

Therefore, in the radio communication system, the wireless communicationmodules 102-1 and 102-2 make it possible to transmit the ACK packets401-1 and 403-1 at the same time.

The synchronizing packets 401-0 to 403-0 makes it possible toperiodically decide a transmission end time of a wireless station inaccordance with a single synchronizing packet even if these packets arenot always periodically transmitted.

The synchronizing packet has a same data structure as that of thecontrol packet shown in FIG. 13 and has time information relating to atiming or duration for ending the reception of the data packet. That is,a synchronizing packet is provided to decide the reception end time of adata packet transmitted by a wireless station. Any informationcontaining the above effect may be provided. For example, instead of thetransmission end time, the time length of the data packet may bepredetermined based on information on only the transmission start time.

The wireless stations 103-1 to 103-m using the same channel as thewireless module 102-2 makes it possible to transmit a packet when thewireless module 102-2 does not transmit an ACK packet if the wirelessmodule 102-1 terminates transmission during a packet-receiving period.

The wireless communication system according to the eighth embodiment ofthe present invention will be described again with reference to FIG. 24and FIG. 25.

A wireless module section 102-1 in a wireless access point has atransmitting/receiving antenna 201, a transmitting/receiving section202, a wireless module control section 203, and a transmissioninformation notifying section 204, as shown in FIG. 21. A wirelessmodule section 102-2 has a transmitting/receiving antenna 205, atransmitting/receiving section 206, a transmission information acquiringsection 207, and a wireless module control section 208.

Now, a signal flow will be described here with reference to FIGS. 24 and25. When a data transmission request occurs with the wireless module102-1, the wireless module control section 203 modulates data into aradio signal via the transmitting/receiving section 202, and transmitsthe radio signal by using the transmitting/receiving antenna 201. Inaddition, the wireless module control section 203 uses the transmissioninformation-notifying section 204, and notifies the transmissioninformation acquiring section 207 of the wireless module 102-2 of thefact that the transmitting/receiving module 202 transmits the radiosignal. The wireless module control section 208 determines that thewireless module 102-1 is transmitting a packet from the transmissioninformation-acquiring section 207. The wireless module control section208 is changed to a state capable of outputting data to thetransmitting/receiving section 206 in response to a signal from thetransmission information-acquiring section 207. Thetransmitting/receiving section 206 transmits a radio signal by using thetransmitting/receiving antenna 205.

As shown in FIG. 24, the wireless module 102-1 transmits data packets601-0 to 601-2, and receives ACK packets 602-0 to 602-2 corresponding tothe data packet. In contrast, the wireless module 102-2 transmitspackets 603-0 and 603-1 so as not to receive the packet of the wirelessstation.

While the wireless module 102-1 is in transmission, when a dummy packetis transmitted by the wireless module 102-2, the wireless station usingthe same channel as the wireless module 102-2 carries out carriersensing, and does not transmit a packet. When the wireless module 102-1is in transmission, the wireless module 102-2 disables reception. Thus,the wireless station using the same channel as the wireless module 102-2makes it possible to reduce wasteful packet transmission.

At this time, the packets 603-0 and 603-1 may have the same time lengthas the packet transmitted by the wireless module 102-1, may be packetssuch that the wireless station physically carries out carrier sensing,or alternatively, may be packets such that information (NAV information)on virtual carrier sensing of the wireless station such as RTS packetsis set.

Further, when the wireless station using the same channel as thewireless module 102-2 makes it possible to receive and determine asignal transmitted by the module 102-1, the wireless station using thesame channel as the module 102-2 makes it possible to know that a packetis not received.

The wireless communication system according to the ninth embodiment ofthe present invention will be described again with reference to FIG. 25.

As shown in FIG. 25, a wireless module 102-1 transmits a data packet701-0. A wireless module 102-2 is so controlled by the controller as todetermine that the wireless module 102-1 is in transmission, and sotransmits a data packet 703-0 as to end the transmission at the sametime as the transmission end time of the data packet 701-0. Thus, thewireless module 102-1 and wireless module 102-2 make it possible toreceive the ACK packets 702-0 and 704-0 at the same timing.

At this time, at the transmission end time of the data packet 703-0transmitted by the wireless module 102-2, while the wireless module102-1 transmits the data packet 701-0, the wireless module 102-2 doesnot receive the ACK packet 704-0. Alternatively, while the wirelessmodule 102-2 transmits a data packet 703-0, a deviation of time ispermitted to an extent such that the wireless module 102-1 does notreceive the wireless station packet.

Apart from deciding the data packet transmission end time, the wirelessmodule 102-2 decides the data packet transmission start time and packettime length, thereby making it possible to achieve the above operation.

A modified example of the wireless communication system according to theninth embodiment of the present invention will be described here.

The wireless module 102-1 and wireless module 102-2 may be so controlledby the control sections 204, 208 as to sense the carries at the sametime, before deciding the data packet transmission start time. Thus, itpossible to set the transmission start times of the wireless module102-1 and wireless module 102-2 to be the same as each other. In thissystem, the wireless module 102-1 and wireless module 102-2 areidentical to each other in time length of a packet to be transmitted,whereby the same transmission end times are transmitted.

Further, while the wireless module 102-1 is in a transmission period,the wireless module 102-2 makes it possible to transmit an ACK packetfree data packet, or alternatively, a broadcast packet or multicastpacket.

Carrying out cooperative operation such that the wireless moduletransmits above synchronizing packet is defined as a synchronous mode.Carrying out operation in autonomous distribution by respective wirelessmodule sections is defined as an asynchronous mode. In the asynchronousmode, a packet error due to bypassing via a transmitting/receivingantenna of a transmission signal between wireless communication modulesis permitted without transmission of a synchronizing packet or the like.

When a large amount of data is to be transmitted/received, the databeing corrected to a time length of a wireless packet, the wirelessmodule 102-1 and wireless module 102-2 decide the fact that abovesynchronous mode is established. In other cases, the asynchronous modeis established. At this time, at the wireless access point, processingis simplified because no control between the modules is carried out. Inthe synchronous mode, a packet can be transmitted/received effectively.Alternatively, it is possible to decide that the above operation iscarried out when the packet time length is small.

In addition, in a wireless communication system as shown in FIG. 26, inwhich traffic statistics of each wireless module 102-1, 102-2 is storedin the traffic processing section 802, a synchronous mode determiningsection can decide the synchronous or a synchronous mode depending onthe traffic state. In the access point 101, the wireless communicationmodules 102-1, 102-2 are controlled by control section 801, and thecontrol section 801 monitors the traffics of the data transmission andreception between the access points and the stations. The monitoredtraffics are supplied to the traffic processing section 802 andprocessed as traffic statistic data, which is stored in the trafficstatistic processing section. The traffic statistic data is sent to thesynchronous mode determining section 803 as a traffic state so that theone of synchronous and asynchronous modes is determined in accordancewith the traffic state in the determining section 803. For example, whensmall traffics are frequently produced, in which relatively small dataitems are transferred between the access point 101 and stations, thedetermining section 803 determines the synchronous mode and sets thewireless communication modules 102-1, 102-2 in the synchronous modes.Thus, transmission/reception of a wireless packet is carried out in acooperative manner in accordance with the synchronous mode, therebymaking it possible to ensure efficient packet transmission. In addition,when large traffics are frequently produced, in which relatively largedata items are transferred between the access point 101 and stations,the determining section 803 may also determine the synchronous mode andsets the wireless communication modules 102-1, 102-2 in the synchronousmodes.

A wireless module has a plurality of different buffers 805-1 to 805-k,as shown in FIG. 27, and the different buffers 805-1 to 805-k are useddepending on the packet time length. In this system, one of thesynchronous mode or asynchronous mode can be selected depending on thepacket time length.

Generally, a data packet to be transmitted by the wireless module 101 isstored in a buffer 805-1. If the wireless module 101 has only one buffer805-1, a plurality of the packets are stored in the buffer 805-1 fortemporarily storing the packets under the control of the control section801. Thus, it is difficult to sample an arbitrary packet from the buffer805-1. However, if the wireless module 101 is provided with a pluralityof buffers 805-1 to 805 l having different buffer size, the data packetcan be stored in one of the buffers 805-1 to 805 l depending on itssize. Thus, if the predetermined data size of the data packet to betransmitted is determined, one of the buffers 805-1 to 805 l is selecteddepending on the predetermined data size so that the data packet havingthe predetermined data size can be selected.

In the wireless communication system, the data packet to be transmittedis input in the control section 401, the packet time length of the datapacket is determined in the packet time length determining section 806.Thus, the control section 401 supplies the data packet to one of thedata buffers 805-1 to 805-k, which has a buffer size corresponding tothe packet time length of the data packet. Accordingly, data packetshaving different packet time lengths are stored in the data buffers805-1 to 805-k. When the wireless module 101-1 transmits one of the datapackets, the control section 801 selects one of the data buffers 805-1to 805-k, in which the one of the data packets to be transmitted isstored. The control section 801 determines whether or not the packettime length of the one of the data packets is larger than predeterminedreference time length. The control section 801 determines one ofsynchronous and asynchronous modes depending on the determination of thepacket time length. That is, if the packet time length of the one of thedata packets is not larger than predetermined reference time length, thecontrol section 801 sets the wireless module sections 102-1, 102-2 inthe asynchronous mode,

In the above-described embodiment, the wireless station in a dependentrelation with the wireless access point decides in random whether or notpacket transmission is enabled/disabled even if a synchronizing packetis received. This makes it possible to avoid packet collision in whichwireless stations receive a synchronous packet and transmits a datapacket at the same time.

In addition, it is possible for the wireless station to decide randomprobability of packet transmission based on the priority (QoS) oftraffics, carrier sensing, and packets.

Where a plurality of wireless stations have received synchronous packet,and such plurality of wireless stations have their respectivetransmission requests, packet collision occurs. Even if the wirelessstation has received the synchronous packet, packet collision can beavoided by deciding whether or not such packet is to be transmitted at arandom probability. The wireless station can acquire traffic informationon the wireless station or wireless access point using the same channel,decide a packet transmission probability, and carry out efficient packettransmission.

The packet transmission probability can be decided from the packetpriority (QoS) to be decided depending on the upper layer.

In addition, if the destination address of the synchronous packetspecifies its own wireless station so as to carry out the specifiedwireless station packet transmission, no packet collision occurs, thusincreasing efficiency. Because of this, the destination address of thesynchronous packet may indicate all the wireless stations or may specifywireless stations in plurality or their own.

A channel to be used by a wireless module may be a periodically adjacentchannel. In addition, as a transmitting/receiving antenna possessed bythe wireless module, there is used an antenna having its directivity.Periodically, the same channel may be used. As a transmitting/receivingantenna, there can be provided an antenna with its variable directivitysuch as adaptive array. There is a case in which wireless module sharesone array antenna, an antenna beam pattern is provided as multiplebeams, thereby transmitting/receiving a radio signal to each wirelessmodule. Because of this, the channels as claimed in claims may bechannels different from each other in frequency or may be such channelsas to accommodate a specific wireless station decided depending on thefrequency and antenna beam pattern.

Apart from each wireless module, a control section is provided in awireless access point, thereby making it possible to achieve synchronousmode operation. At this time, operation of wireless communicationmodules M1 and M2 is decided depending on the control section in thewireless access point irrespective of the wireless communication modulesM1 and M2.

The system according to an aspect of the invention is not limited to thewireless communication system of the access point and the stations, asshown in FIGS. 1 and 20. It is apparent that this invention can beapplied to a system in which wireless communication stations 1-1, 1-2are provided with adaptive array antennas 2-1, 2-2, respectively, asshown in FIG. 28. The wireless communication stations 1-1, 1-2, shown inFIG. 28, comprises receivers 11-1 to 11-3 and 11-4 to 11-6, transmitters12-1 to 12-3 and 12-4 to 12-6, reception end timing detecting sections18-1, 18-2, and transmitting enabling sections 19-1, 19-2, in a samemanner as that of the wireless communication system.

As shown in FIG. 29, it is possible to apply this invention to acommunication system, which is provided with wireless communicationstations 1-1, 1-2. The with wireless communication stations 1-1, 1-2 isprovided with antennas 91, 92, instead of the adaptive antenna array2-1, 2-2, for receiving and transmitting adjacent channels 1 and 2 ascarriers, and switching units 93, 94 for switching between transmitters11-1, 11-2, 11-3, 11-4 and receivers 12-1, 12-2, 12-3, 12-4.

The wireless communication system, shown in FIG. 29, has a same functionand is operated in a same manner as that of the above describedembodiments, except for provision of the switching unit 93, 94 whichconnect the antennas 93, 94 to the transmitters 11-1, 11-2, 11-3, 11-4,in the transmission mode, respectively, and connect the antennas 93, 94to the receivers 12-1, 12-2, 12-3, 12-4, in the reception mode,respectively.

As has been described, According to an aspect of the present invention,there is provided a wireless communication station capable of properlycarrying out transmission/reception between the wireless communicationstation and another wireless communication station.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A wireless communication apparatus for receiving first and second reception signals from at least one of wireless communication units and transmitting first and second transmission signals to at least one of the wireless communication units, comprising: a receiving portion including first and second receiver modules configured to receive the first and second reception signals from at least one of the wireless communication units; a transmission portion including first and second transmitter modules configured to transmit the first and second transmission signals to at least one of the wireless communication units; and a control portion configured to control the transmission portion so as to transmit the first and second transmission signals from the first and second transmitter modules at a transmitting timing which is so determined to have an elapsed time period after the reception end of the first and second reception signals in the first and second receiver modules, the elapsed time period being determined in accordance with a random probability.
 2. The wireless communication apparatus according to claim 1, wherein the first and second transmission signals have a same transmission period during which the transmission of the first and second transmission signals are completed.
 3. The wireless communication apparatus according to claim 1, wherein the wireless communication units include first and second wireless communication units, and the first and second receiver modules receive the first and second reception signals from the first and second wireless communication units, respectively.
 4. A wireless communication apparatus for receiving first and second reception signals from at least one of wireless communication units and transmitting first and second transmission signals to at least one of the wireless communication units, comprising: a receiving unit including first and second receiver modules to receive the first and second reception signals from at least one of the wireless communication units through first and second adjacent channels; a transmission unit including first and second transmitter modules configured to transmit the first and second transmission signals to at least one of the wireless communication units through one of the first and second adjacent channels or through the first and second adjacent channels; and a control unit configured to control the transmission unit so as to transmit the first and second transmission signals from the first and second transmitter modules at a transmitting timing which is so determined to have an elapsed time period after the reception end of the first and second reception signals in the first and second receiver modules, wherein the control unit determines the elapsed time period in accordance with a random probability.
 5. The wireless communication apparatus according to claim 4, wherein the first and second transmission signals have a same transmission period during which the transmission of the first and second transmission signals are completed.
 6. The wireless communication apparatus according to claim 4, wherein the wireless communication units include first and second wireless communication units, and the first and second receiver modules receive the first and second reception signals from the first and second wireless communication units, through the first and second adjacent channels, respectively.
 7. A wireless communication apparatus according to claim 4, wherein the first and second transmitter modules set transmission start times to be the same as each other.
 8. A wireless communication apparatus according to claim 4, wherein the first and second transmitter modules transmit the first and second transmission signals at the same time.
 9. A wireless communication apparatus for receiving first and second reception signals from at least one of wireless communication units and transmitting first and second transmission signals to at least one of the wireless communication units, comprising: a receiving unit receiving the first and second reception signals from at least one of the wireless communication units through first and second adjacent channels; a transmission unit transmitting the first and second transmission signals to at least one of the wireless communication units through one of the first and second adjacent channels or through the first and second adjacent channels; and a control unit controlling the transmission unit so as to transmit the first and second transmission signals from the transmission unit at a transmitting timing which is so determined to have an elapsed time period after the reception end of the first and second reception signals, wherein the control unit determines the elapsed time period in accordance with a random probability.
 10. A wireless communication apparatus according to claim 9, wherein the transmission unit sets the transmission start times to be the same as each other.
 11. A wireless communication apparatus according to claim 9, wherein the transmission unit transmits the first and second transmission signals at the same time.
 12. A wireless communication apparatus for receiving first and second reception signals from at least one of another wireless communication apparatus and transmitting first and second transmission signals to at least one of the another wireless communication apparatus, comprising: a first wireless unit configured to receive the first reception signal from at least one of the another wireless communication apparatus through a first channel and transmit the first transmission signal to at least one of the another wireless communication apparatus through the first channels; a second wireless unit configured to receive the second reception signal from at least one of the another wireless communication apparatus through a second channel adjacent to the first channel and transmit the second transmission signals to at least one of the another wireless communication apparatus through the second channel; and a control unit configured to control the second wireless units so as to transmit the first and second transmission signals from the second wireless unit at a transmitting timing which is so determined to have an elapsed time period after the reception end of the first and second reception signals, wherein the control unit determines the elapsed time period in accordance with a random probability.
 13. A wireless communication apparatus according to claim 12, wherein the first and second wireless units sense carriers at the same time.
 14. A wireless communication apparatus according to claim 12, wherein the first and second wireless units set the transmission start times to be the same as each other.
 15. A wireless communication apparatus according to claim 12, wherein the first and second wireless units transmit the first and second transmission signals at the same time. 